The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
An operating cycle of an internal combustion engine may include a plurality of engine strokes. For example, an operating cycle may include four different engine strokes. In an “intake stroke,” the engine may draw air into a cylinder through an intake manifold and an intake valve. The air may then be mixed with fuel to form an air-and-fuel (A/F) mixture. In a “compression stroke,” the A/F mixture may be compressed by a piston within the cylinder.
In a “power stroke,” the compressed A/F mixture may be combusted by a spark plug within the cylinder to drive the piston, rotatably turning a crankshaft to generate engine power. In an “exhaust stroke,” exhaust gas produced by the combustion of the A/F mixture (i.e. during the power stroke) may be expelled from the cylinder through an exhaust valve and an exhaust manifold.
The operating cycle may also be divided into an “expansion cycle” and a “non-expansion engine cycle. More specifically, the non-expansion cycle may include the intake stroke and the exhaust stroke (i.e. the pumping strokes) and a first portion of the compression stroke. Alternatively, the expansion cycle may include a remaining portion of the compression stroke and the combustion stroke. In other words, the non-expansion cycle may include the strokes (or portions thereof) where negative work occurs (i.e. where heat is not released by combustion).
“Virtual” (i.e. soft) cylinder pressure sensors may estimate a pressure in a cylinder based on various engine parameters. However, virtual cylinder pressure sensors may be inaccurate due to the energy losses (i.e. pumping losses) during the non-expansion engine cycle. Referring now to FIG. 1, a graph illustrating the inaccuracy of conventional virtual pressure sensors is shown. The graph includes pressure traces from an instrument quality sensor (i.e. approximately the actual pressure) and from a production quality virtual pressure sensor. As can be seen, the production quality virtual pressure sensor measurement is typically 20-40 kPa different than the instrument quality pressure sensor due to increased noise during the non-expansion engine cycle. Furthermore, at one point, the production quality virtual pressure sensor measurement is more than 80 kPa different than the instrument quality pressure measurement.